In January 1996, parts of Virginia recorded up to four feet of snow
during a record-breaking blizzard. When the Blizzard of 1996 was over,
nine states had declared a state of emergency. One hundred people were
dead.

Blizzards such as this one are the most severe
forms of snowy weather, with winds of 35 miles per hour or greater
and visibility of less than 1/4 mile. Winter storms and blizzards
may not always be as dramatic as the one that blanketed the northeastern
United States in 1996, but their potential to disrupt everyday activities
is great. Schools close. Commerce is interrupted. Property damage
can occur from flooding or structural collapse. These storms may not
rival hurricanes or tornadoes in destructive power, but they are an
effective annual reminder of our planet's dynamic climate.

How does snow form?

Snow
begins in the atmosphere as water condenses into a tiny droplet. As
more and more water vapor condenses onto its surface, the droplet
grows. Cold air then freezes this water into an ice crystal.

Each ice crystal has a unique shape that depends on the surrounding
air's temperature and water vapor content. If it is below freezing
and there is a lot of water vapor in the air, the crystal grows six
evenly spaced branches. More and more water vapor collects
on these branches and freezes, making the ice crystal increasingly
heavy. Eventually, the ice crystal falls from the sky, leaving the
cloud of precipitation that it helped to form. As it falls, the crystal
continues to grow by picking up more water vapor.

As it descends, the ice crystal can come into contact with warmer
air that makes it melt somewhat. This melting acts like a glue, causing
crystals to bond together into larger flakes, forming what many people think
of as the "classic" fluffy snowflake. If the crystals melt too much and
then refreeze as they get closer to Earth's surface, the precipitation falls
as sleet instead of snow.

Once on the ground, snow will remain if temperatures are cold enough
to keep it from melting. Glaciers that form on mountains, for example, are made up of snow that accumulates
on the ground and eventually turns to ice.